Bending Point Research Articles

Effects of italicized angle and turning angle on shale gas nanoflows in non-straight nanopores: A nonequilibrium molecular dynamics study

Non-equilibrium molecular dynamic simulations were performed to investigate the effects of the italicized angle and turning angle of non-straight nanopores on the flux of shale gas, with considering smooth and rough porous surfaces respectively. First, the flux data in smooth nanopores are always larger than that in the rough because the rough surface results in the stronger adsorption and slower flow-velocity profiles than the smooth. Second, the italicized angle promotes the methane flow for both smooth and rough nanopores. It is explained that the energy barrier located at the entrances of nanopores reduces with increasing the italicized angle. Moreover, the average Lennard-Jones (LJ) potential of nanopores, a resistance for particles across these nanopores, also weakens with the angle. Third, however, the turning angle shows different effects depending on the roughness. It impedes the methane flow in smooth nanopores but promotes the flow in rough nanopores. The decisive factor lies in the energy barrier locating at the bending point, which plays a prominent impeding impact in smooth nanopores but unapparent in rough nanopores, while the average LJ potential commonly promotes the flow for both surfaces with increasing the turning angle. To the best of our knowledge, this is the first reported study clearly distinguishing the effects of italicized angle and turning angle on nanoflow. These observations are very useful for understanding the transport of shale gas in tortuous porous networks in shale as well as the flow in carbon nanotubes.

An image analysis-based method for automatic data extraction from pilot draining experiments

ABSTRACT An image analysis-based method is developed to automatically interpret videos of a transparent Hele-Shaw model in studies of blast furnace hearth drainage in pilot scale. By the approach, information from experiments can be extracted for quantitative assessment of the draining phenomena. The algorithm consists of modules for (1) image pre-processing, (2) interface tracking, and (3) bending-point detection. The pre-processing step makes preparatory estimates for the next module that extracts the liquid–gas and liquid–liquid interfaces. Finally, bending points of the interfaces are detected and parameters quantifying the interface bending are calculated. The algorithm is illustrated by applying it to a video of a draining experiment, demonstrating how information can be extracted. The method can be used to compile information from a large set of experiments to gain a deeper understanding of the complex two-phase flow in the blast furnace hearth and to quantify the findings for a validation of computational models.

Investigating Role of the Hormuz Salt Bodies in Initiation and Evolution of the Strike Slip Faults in the Fars Zone of the Zagros Fold and Thrust Belt: Insights from Seismic Data and Sandbox Modeling

The Zagros Belt has examples of strike-slip faults affected by precursor Hormuz Salt bodies. We attempted to examine the role of salt walls in localizing the strike-slip faults using field observations, seismic profiles and understandings from the sandbox modeling. Setting and performance of the pre-Hormuz features in connection to the salt tectonics are major questions. The inherited topography below the salt is an important parameter which controlled the structuration of the basin. The antecedent troughs provided accommodation for the thick Hormuz Salt. Differential loading above the salt helped generation of salt-related structures. The salt-walls caused formation of elongated highs. These highs were re-shaped in form of strike-slip faults during the Zagros Orogeny. The intersection of the salt walls and the Zagros-induced deformation fronts are location of potential diapirs needless of bending points along the tear faults. In contrast, the underlying deep-seated basement faults are hardly believed to be strike-slip.

Experimental study of nanoparticle transport and penetration efficiency on a sharp-bent tube (elbow connection)

In the present study, nanoparticle transport through a sharp-bent tube, i.e., elbow connection, was systematically examined by using a particle size ranging from 3 to 50 nm. In the experiments, particle size and flow rate significantly affected the penetration efficiency. To be specific, the smaller particles which had higher diffusion coefficient were more likely deposited on the sharp-bent tube and the higher flow rate reduced the flow-directional nanoparticle residence time resulting in increased penetration efficiency. To explain the experimental penetration efficiency on the sharp-bent tube, characteristics of fluid flow on the sharp-bent tube were studied numerically. The flow field calculations showed that the recirculation pattern occurred at the corner of the sharp-bent tube, and the flow separation and reattachment were observed at the inner wall right after the bending point. Additionally, when compared to higher Reynolds number, the intensity of the secondary flow was weaker at lower Reynolds number as well as its center point was located farther from the tube wall. Therefore, the nanoparticle residence time on the sharp-bent tube became longer and a smaller number of particles penetrated the tube at lower Reynolds number. Based on the experimental data, the penetration efficiency on the sharp-bent tube was predicted by the correlation fitting curve. The relative penetration efficiency on the sharp-bent tube was also obtained by comparing it to the penetration efficiency on the straight tube. The strong diffusion transport rate and weak advection transport rate induced more particle losses due to secondary flow after bending point, resulting in the decreased relative particle efficiency.

Kinetics and Thermodynamics of Adsorption–Desorption of Water Vapors on Microsized Powders of Layered Molybdenum Disulfide

Experimental kinetic data on the adsorption and desorption of water vapors on molybdenum disulfide in relative humidity ranges of the gas phase from zero to 100% are presented. Microsized layered molybdenum disulfide powders (manufactured by Climax Molybdenum Co., USA) were used in the experiment. The adsorption–desorption kinetics of water vapors was studied by the gravimetric method. In the continuous automatic mode, the weight changes in the test sample and the process rate were recorded. An air stream with a relative humidity of 100% was used for water vapor adsorption. Desorption was studied under decrease in the partial pressure of air flow water vapors to 55% of the relative humidity in isothermal and nonisothermal conditions (temperature increase and decrease in the range 20–130°C). The time dependence of the adsorptive process of water vapors in a flowing system with 100% humidity of the gas phase is close to parabolic. The dependence of adsorption on water vapor pressure (V = f(Pi) is S-shaped with the bend point in the region of transition to condensation-induced filling of absorption volumes. The desorption rate exceeds the adsorption rate. The adsorption potential theory of Polanyi, Dubinin, and Radushkevich was used to assess the bonding energy between the water molecules and nonuniform MoS2 porous structure. The change in the adsorptive forces and the Pi/Ps ratio depending on the change in adsorbate volume were characterized. Adsorption isotherms for water vapors were plotted at 30 and 50°C. The graphical integration method was applied to determine the differential rate of forming the water adsorption volumes (dVi) at water partial pressures 0 < Pi < 5 kPa. The kinetic features of the stepwise process are shown to depend on the potential energy of interaction between the adsorbed volumes and adsorbent. The nature of the adsorption process does not change in temperature changes. The coordinates of intensive formation of the adsorption volume changed towards increase in the partial pressure of water vapors.

Effect of water-cement ratio on fracture energy based on work of fracture

Concrete is brittle material which generally consists of many micro cracks which are a potential source of crack propagation which leads to possible catastrophic failure and resulting fracture of concrete structures under service loads. The relationship of fracture energy to material properties has not been clearly identified, with most studies showing a relative insensitivity to the water-cement ratio, and concrete cracks propagate mainly along the aggregate-cement interface. This research is an experiment about the effect of water-cement ratio on fracture energy based on the RILEM method. The fracture energy is measured by testing under three bend points with the notch depth ratio is 0.25 and loading rate is 0.05 mm/sec using a closed-loop testing machine to produce load-displacement curve. Concrete used crushed stones with a maximum size of 19 mm which was tested at 56 days of age and has a water-cement ratio (w/cm) of 0.30, 0.40 and 0.6. The correlation between fracture energy and water-cement ratio are insensitive to each other. This can be seen when concrete containing a lower water-cement ratio (0.3) tends to have increased compressive strength but decreases fracture energy.

Investigation of the influence of the gas pipeline tee geometry on hydraulic energy loss of gas pipeline systems

CFD simulation investigated turbulent flows in equal gas pipeline tees, in which the gas flow completely moves from the main line to the branch. The study was performed for tees of different geometry – stamped with different bending radii of the transition from the branch to the main line and weld, where the main line and branch connection is made at right angles. The outer diameter of the tees varied from 219 mm to 1,420 mm, the bending radius of the transition from the branch to the main line from the minimum permissible to the maximum possible, the pressure in the gas pipeline at the tee location from 3 MPa to 7 MPa. The mathematical model is based on the solution of the Navier-Stokes and energy transfer equations closed by a two-parameter high-Reynolds k – e Launder-Sharma turbulence model. To describe the processes occurring at the wall, the wall function was used. It was found that the bending of the transition from the branch to the main line, the increase in the bending radius lead to a decrease in the intensity of flow separation at the bending point and a decrease in turbulence kinetic energy in recirculation areas. The velocity field of the gas flow after it moves from the main line to the branch becomes more uniform. All this greatly affects the magnitude of hydraulic energy loss of the gas flow in the tees. In this case, the greatest energy losses were observed in the tees located at the lowest pressure points in the gas pipeline system. An analysis of the results showed that if the ratio of the bending radius of the main line and branch connection to the outer diameter is more than 0.25, then the influence of such a tee on the energy loss of the gas pipeline system is minimal. Local resistance coefficients of equal gas pipeline tees are calculated and the resulting equation for their calculation will be useful for specialists designing gas pipeline systems

Mechanical Behavior &amp; Analysis of Epoxy, Al2O3 Composites

In this paper, an intelligent report has been planned for to assess epoxy composite network Epoxy composite execution of Al2O3 particles remembered for epoxy composite resin. A ultrasonic blending method applied to accomplish homogenous dissemination of particles addicted to epoxy pitch. Various mechanical and Tribological tests, for example, bending (three(3) point) test, Charpy Impact test &amp; hardness are perform to check mechanical properties &amp; wear execution of Al2O3+ Epoxy composites. These composites showed expanded bowing quality and effect quality because of the absorption of Al2O3 particles. In collection, presentation of Al2O3 particles into Epoxy gum grid at low qualities brought about noteworthy decrease of wear rate Such type of impacts would be ascribed to the scattering of Al2O3 particles into epoxy framework &amp;stacking. The impact of the Al2O3 molecule ejection with epoxy lattice tar is additionally portrayed regarding strengthening strategies.

Analysis of the main factors affecting bottom hole assembly Re-entry into main hole in forward drilling of fishbone wells

Wellbore re-entry is one of the critical technologies in fishbone well drilling. In the sequence of forward drilling, the main hole is designed as a low wellbore and the branched hole is designed as a high wellbore to ensure that the bottom hole assembly (BHA) can re-enter the main wellbore. However, there is no quantitative theoretical analysis regarding the reliability of wellbore re-entry at present. In order to analyze the reliability of the main hole re-entry, an analysis method was provided in this paper. Firstly, a detailed description of the wellbore model around the sidetracking point was built, which can consider the different build-up rate and bending direction of the main and branched hole. Secondly, a mechanical model based on the elastic rod theory was established to calculate the force and deformation of drill strings in the wellbore and a re-entry coefficient was introduced to evaluate the reliability of the main hole re-entry. Moreover, the effects of tool face angle, build-up rate of wellbore, junction wall geometry, and motor structure on the re-entry coefficient are analyzed. Finally, the main controlling factors were analyzed to distinguish the influence degree of different parameters on the re-entry coefficient. From the results, the angle between the bending direction of the branched hole and the tool face of the BHA is the decisive factor in the process of the main hole re-entry. The BHA should be controlled so that the angle is greater than 90° as much as possible. If such angle is less than 90°, the change of wellbore build-up rate, junction wall geometry, and motor structure can be used to increase the re-entry coefficient, such as increasing the build-up rate of the branched hole, wellbore enlargement rate, depth of the slot in the junction wall, and ridge width of the junction wall. Meanwhile, decrease the angle of bent housing, distance between the bending point and the top of bit, and outer diameter of the body stabilizer of the motor can also increase the re-entry coefficient. Among the effects of re-entry coefficient, the main controlling factors are the bend point position and the angle of bent housing.

Resolving the nanostructure of sodium carbonate extracted pectins (DASP) from apple cell walls with atomic force microscopy and molecular dynamics

The diluted alkali-soluble fraction of the cell wall pectic matrix extracted with sodium carbonate (DASP) from apple fruit (M. domestica cv. Golden Delicious) was subjected to extensive analysis aimed at refining the current view concerning its molecular structure. Pectins were examined by means of atomic force microscopy (AFM) and HPLC chemical analysis. In addition to this, computational chemistry was employed to characterize the structural features of the basic plant cell wall polysaccharides and their possible assemblies. The AFM imaging revealed that DASP molecules deposited on mica structurally resembled rod-like objects, consisting of relatively long linear sections separated by bend points or branches. Locally molecules also formed aggregates, which were visible as an amorphous phase, concentrated around linear sections. Based on chemical analysis combined with molecular dynamics (MD) the linear chains were identified as sections of unbranched homogalacturonan, while the second most abundant polysaccharide present in DASP – arabinose – was considered to constitute the amorphous aggregates. The study showed that despite being present in small amounts, rhamnose is an important factor affecting the formation of the characteristic shape of DASP molecules on mica. The structural characterization of the bend points showed that linear molecules oriented at specific angles are most likely to be formed by two sections of homogalacturonan separated by a single rhamnose unit. AFM images confirmed that this is a common feature of the molecular structure of the DASP fraction, suggesting a possible role in the networking of pectic polysaccharides. Rhamnose interspersions within the homogalacturonan chains lead to the formation of spatial structures, which resemble kinked rods with segments having the ability to change their relative positions. The higher mobility of the linear sections as well as the higher number of segments increases the number of possible interactions with surrounding molecules and thus increases its ability to form gels. Therefore, it is expected that the number of rhamnose units and the length of the linear homogalacturonan sections will be one of the factors that influence the gelling abilities of pectin. Furthermore, it was proposed that branch points are created, similar to bend points, by single interspersions of rhamnose, which connect three homogalacturonan chains or short sections (two or three dimers) of rhamnogalacturonan-I with a homogalacturonan side branch. The third proposed alternative was a complex of two adjacent homogalacturonan chains, one of them having a single rhamnose insertion causing a bend in the structure.

Suitable methods of measuring acceleration time in the diagnosis of internal carotid artery stenosis

PurposeTo enhance the utility of acceleration time (AcT) in the diagnosis of internal carotid artery (ICA) stenosis, we assessed the value of AcT measurements with different waveform patterns.MethodsNinety-three patients with acute atherothrombotic cerebral infarction were enrolled, and they underwent both carotid ultrasonography and digital subtraction angiography (DSA). AcT was determined by a conventional procedure (using the first peak point or the bending point) and the peak systolic velocity (PSV) procedure. The AcT ratio was calculated as (AcT of ICA)/(AcT of the ipsilateral common carotid artery). We evaluated the correlation of stenosis rate as assessed by the North American Symptomatic Carotid Endarterectomy Trial method using DSA (DSA-NASCET) with the AcT of ICA (ICA-AcT), the AcT ratio measured by the conventional procedure (conventional AcT ratio), and the AcT ratio measured by the PSV procedure (PSV AcT ratio). The area under receiver operating characteristic curves (AUC) for DSA-NASCET was calculated based on the ICA-AcT and AcT ratio.ResultsForty-five vessels had 50% or greater ICA stenosis. DSA-NASCET was positively correlated with the conventional AcT ratio (r = 0.723), conventional ICA-AcT (r = 0.638), and PSV AcT ratio (r = 0.245). The corresponding AUCs for ICA stenosis ≥ 50% were 0.971, 0.886, and 0.572, respectively.ConclusionWe demonstrated the usefulness of the conventional procedure for diagnosing stenosis of ICA origin using AcT and showed that the AcT ratio was a more beneficial parameter than AcT.

Dynamic analysis of a rotating stepped shaft with and without defects

Rotating machines have many applications, in several mechanical systems. They typically contain a rotary shaft as an influence conversion unit, that is subject to multiple loads in operation. One of the most widely-used rotary machines is the pump, and pump shafts are exposed to many forces due to fluids, unbalancing due to slight bending in the shaft or errors of design or bearings, bearings-induced forces, etc. These forces can reach an unacceptable level once the rotor is functioning close to its natural frequencies. Excessive vibration levels within the device cause fatigue and thus tiny cracks may grow to a serious extent and ultimately cause failure. In this study, dynamic analysis of the pump shaft was made, with and without cracking. Fundamental bending natural frequencies and torsional natural frequencies, response shaft, the equivalent stresses and total deformations in each dynamic and static cases were evaluated. The dynamic load factor (DLF) was calculated in the presence of cracks of various depths (4mm, 6mm, 8mm, 10mm, 12mm) set at diverse locations (x=80mm, x=166mm, x=210mm) measured from the point of overhanging. The finite element method by ANSYS package was used to conduct the numerical analysis for this study, and a specific experimental test rig was built to verify the experimental results. Results showed that increasing depth of the cracks will lead to reducing in the natural frequency and, as a result, increase instability in the shaft. When the location of the crack is close to the highest bend point in the shaft, the natural frequencies will increase. In addition, the equivalent stress depends on cracking location and it is increased with increased depth of cracking.

Apokamp-type gas discharge phenomenon: Experimental and theoretical backgrounds

The apokamp discharge is an atmospheric pressure plasma jet generating from the bending point of the discharge channel between high-voltage and floating potential electrodes. The jet propagates perpendicularly to the interelectrode discharge channel for several centimetres without gas convection. Based on the simplified plasma-chemical model of the discharge, a theoretical explanation of the apokamp phenomenon was obtained for the first time. It is shown that the apokamp is a stable plasma quasi-jet formed by the positive streamer mechanism.

Effective Gyroresonance Layers in the Transition Region of the Active Region of the Solar Atmosphere. Magnetic Fields and Heights

Abstract—We present a method of determination of numbers of gyroresonance layers most effectively radiating in the transition region of the active solar atmosphere. It is based on determination of frequency in the spectrum of an extraordinary wave of an active region, at which the gradient of this spectrum abruptly rises. Observations of 29 active regions carried out at the RATAN-600 radio telescope have been analyzed. The magnetic field in the transition region was determined from the frequency of bending point in the spectrum of antenna temperatures in an extraordinary mode under condition of emission in the third harmonic of the gyrofrequency. The relation between the photospheric magnetic field strength and the magnetic field strength in the transition region (1.52–2.28) is substantially greater than previously obtained, namely, the field isdecreasedonlyby10–20% in the transition region. The heights in the transition region were determined from the reconstructed magnetic field in the nonlinear force-free approximation, and are in the range of 1.00–3.57 Mm.

Laboratory Simulation of Blue Jets with Apokampic Discharge in the Hz Frequency Range

It is shown that the channel of apokampic discharge is a source of streamers at low air pressure and low frequencies (7–16 Hz) of high-voltage positive-polarity pulses and voltage amplitudes from 26 to 35 kV. The maximal starting speed of laboratory streamers was 560 km/s. A hypothesis about blue jet origination in nature is suggested based on experimental data. For their start, high frequencies of voltage pulses are not required, breakdowns in the Hz range are sufficient, but the discharge channel should bend and the field intensity should be high at the bending point.

Apokampic Discharge: Formation Conditions and Mechanisms

The experimental and theoretical investigations of a new form of burning of a repetitively-pulsed discharge – apokamp – are performed. It is shown that an apokampic discharge represents a narrow streamer channel, growing from the point of plasma channel bending, having a characteristic propagation velocity of tens and hundreds of meters per second, depending on the applied voltage and gas pressure and type. The conditions necessary for an apokamp to evolve are formed in a comparatively weak macroscopic electric field. The channel bend ensures a local field enhancement, which prescribes the starting orientation of the growing streamer channel. The pulse-frequency power supply regime of the discharge reproduces the streamer channel in every pulse, but the preceding framework of the ion-ion plasma ensures reproduction of the channel shape from pulse to pulse.

Application of artificial neural networks to predict flow velocity in a 180° sharp bend with and without a spur dike

This work has compared the performance of three well-known artificial neural network (ANN) approaches in turbulent flow pattern modeling based on geometric characteristics of the channel (angle of horizon, distance from outer bank of the bend, and distance from the bed) in a 180° sharp bend with and without a T-shaped spur dike. ANN methods discussed in this work are feed-forward neural network, cascade feed-forward neural network, and extreme learning machines. Acoustic Doppler velocimetry is used to measure the velocity components in x, y, and z directions. Conducting this research is innovative and significant from three aspects: First, the data of the flow pattern around T-shaped spur dikes in a 180° bend, given its high importance in rivers in nature, are very rarely available; second, application of neural network models for understanding the flow nature is highly efficient at other bend points where no experimental or field measurements have been conducted; and third, with these models, the cost and time required for conducting numerical and experimental modeling for prediction of the flow velocity significantly decrease. Outliers (abnormalities or anomalies) may be generated by various factors in the measured velocities. Before modeling by ANNs, the self-organizing map clustering method is used to detect outliers to obtain more accurate models. Performance of ANN models is evaluated using correlation coefficient (R) and root mean squared error criteria. In order to compare the performance of ANNs in flow velocity modeling at different locations of the bend, seven different data groups are considered using different combinations of samples by random sampling. Results of comparison of ANN models with experimental data indicate that ANNs provide reasonable results in most cases and may be employed successfully in estimating the velocity in sharp bends with and without the presence of a spur dike. Moreover, it may be concluded that ANN models without spur dikes are more accurate than those with spur dikes due to creating less turbulence flow.

Effect of Caponisation on Bone Development in Native Male Chickens

Abstract The aim of the study was to determine the effect of caponisation on the morphometric traits and mechanical parameters of tibial and femoral bones in Greenleg Partridge cocks. The experiment involved 200 cocks. At the age of 8 weeks, 100 birds were subjected to surgical castration. At week 24, the birds were slaughtered and tibial and femoral bones were collected from 10 non-caponised cocks and 10 capons. The caponisation surgery had no effect on the weight and length of any of the long bones but resulted in reduction (P≤0.05) of the ash content in both bones and Ca in the femur. It also influenced the geometric structure of the bones, i.e. there was an increase (P≤0.05) in the second moment of inertia in the tibial bone and the cross-sectional area and mean relative wall thickness in the femoral bone of the capons. The three-point bending test revealed a negative effect of caponisation on the mechanical strength of the bone. Values characterising the highest bone material strength, i.e. yielding load (femur), maximum force moment (tibia) and yielding deformation, bending point resistance, and load-to-deformation (both bones), declined in the capons. The investigations demonstrated a negative effect of caponisation on the quality of long bones. The tibial bone seems to be slightly more sensitive to the caponisation effects than the femoral bone. It can be assumed based on the analysis of biomechanical traits that the bones of capons are more susceptible to deformations or fractures due to their modified geometry and mechanical brittleness.

Особенности токовой перегрузки в автомобильной электрической сети

Introduction. The data given in the article show that the problem of fire safety in motor vehicles is highly relevant. The purpose of the article is to develop a scientifically based method of research for the copper conductor exposed to overcurrent to find the reason of its damage when making a fire investigation. Materials and methods . The research was conducted using the JSM-6390LV scanning electron microscope for energy dispersive spectroscopy. The surfaces of the copper conductor rupture were analyzed without any preliminary sample preparation. Results and discussion . The analysis of the experimental evidence demonstrates that the temperature of the copper conductor exposed to current overload varies significantly along its length. It was found through the field studies and experimental results that the rupture of the copper conductor under the action of overcurrent happens in the sections that have prestress due to the plastic deformation. The experiment proved that the formation of ball fusing of the copper conductor exposed to current overload may take place at a substantially lower temperature than that of the copper smelting. The analysis of the theoretical data shows that during the current overload not only thermal and electromagnetic processes but also plastic distortion occur at the copper conductor. It also demonstrates that the strand connection of copper wires results in a fire hazard not in every instance. Conclusion . A method for differentiating fire damages at the copper conductor (current overload, short circuit) was suggested. The current overload has such features as blistering or ball fusing in the bending points and the lack of any signs of mass transfer. It was found that the features of the damaged surfaces of the copper conductor exposed to overcurrent are stable and not subject to changes in the natural storage conditions. The data given in the article can be used by specialists when making an expert examination of copper conductors from the fire locations, identifying a mechanism for their damage and, finally, a cause of fire.

Morphologic Changes of the Femoropopliteal Arterial Segment with Knee Flexion after Endovascular Therapy.

Objective: The purpose of this study is to investigate morphologic changes of the femoropopliteal arterial segment (FPAS) with knee flexion after endovascular therapy (EVT).Methods: From July 2012 to January 2015, EVT was performed on 12 limbs in 12 consecutive patients who had obliterative lesions in the FPAS. After the implantation of nitinol stents, angiography was performed with the knee in both extension and flexion to investigate morphologic changes of the FPAS.Results: On angiography, the distal end of the implanted stent was placed at various distances (5–10 cm in two cases, 10–15 cm in nine cases, and 15–20 cm in one case) above the knee joint line with the knee in extension. In all cases, although the popliteal artery was highly bent with the knee in flexion, the FPAS morphology was highly variable. However, the most proximal bending point of the FPAS was about 10 cm above the knee joint line. In one case, the artery was occluded at the distal part of the stent 16 months later, probably due to EVT.Conclusion: In EVT of the FPAS, it is important to consider the characteristics and position of the stent to prevent complications.